How do I stop overthinking?

Thanks for your message. Overthinking is a common difficulty and I am sure that there will be comfort for others to see both your honesty and the response. 

From what you say, it sounds like you have already developed some strategies for coping with your overthinking, as this is familiar to you from your upbringing, I get this from reading '...it runs in my family but I have learned to semi deal with these'. It may be helpful to look at what your current coping strategies are, if these are healthy and serving you and what new strategies you might introduce. Seeking out some CBT (Cognitive Behavioral Therapy) may be helpful for you to explore your compulsive and intrusive thoughts as this works by looking at how our thoughts impact our behavior and how to 'retrain' yourself to think differently. CBT can also work on decatastrophizing and making sense of intrusive thoughts.

Long term talking therapy may be helpful for you to explore how you have internalized messages from childhood and to look at what it was like for you to experience growing up around others who were having difficulties with intrusive thoughts.

As a cancer survivor it is understandable, as you say, that you would have some health anxiety around this and worry about how your body is behaving and the messages it is giving to you. It is really positive to hear your self compassion here as you acknowledge the root of this. It sounds as though you have developed a hypervigilance here for threat. Cancer is of course a threat to your health and I imagine it was a shock to discover this was your diagnosis? It sounds as though you are perhaps stuck in this alert state looking out for danger. I wonder if you felt a sense of 'missing something' in the lead up to your diagnosis? This can lead to a place of alertness, looking out for danger and threat at every corner. You describe an alertness for having upset someone or overthinking your partner's responses to you, perhaps trying to 'stay on top of the game' and be vigilant for what might be around the corner. This sounds really tiring.

Longer term talking therapy could help you to explore more deeply the patterns of behavior you are experiencing here and shed light on what may have led to your current discomfort around over thinking. Once we are able to see our patterns of behaviour more clearly we are able to understand them and take charge so we can act differently and make positive changes in our lives. Well done for reaching out and seeking support for this, you are not alone. Posing your question and asking for help is the first step towards making the changes you seek.